Question

Tyrosine is a precursor of which of the following?
A) Melanin
B) Epinephrine
C) Norepinephrine
D) All of the above

Answer 1

Hint: Many biomolecules are polyfunctional. They contain two or more various types of functional groups, each with its own chemical characteristics and reactions. Amino acids are an important type of biomolecules. Amino acids contain two different types of functional groups: a carboxylic group and an amino group. Tyrosine is an alcoholic group. It contains amino acids.

Complete answer:
Tyrosine is an organic compound, and one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein, which is not essential to the human diet, since it can be synthesized in the body from phenylalanine. Phenylketonuria occurs when the enzyme that catalyzes the transformation of phenylalanine to tyrosine is not active because of a hereditary defect. The rare hereditary disorder known as alkaptonuria, (discharge of urine which darkens on standing exposed to air) is also a side effect of tyrosine metabolism. Tyrosine is a precursor of epinephrine and norepinephrine, the thyroid hormones, including thyroxine. Melanin is also derived from this amino acid. Tyrosine gives rise to a family of catecholamines that includes epinephrine, norepinephrine and dopamine. Hydroxylation of phenylalanine produces tyrosine. It is also the precursor of the hormones norepinephrine and epinephrine, secreted by the adrenal medulla.
Thus, the right option is D.

Note: Tyrosine residues in enzymes have frequently been found to be associated with active sites. With the help of different chemicals, modification of these residues results in total destruction of its activity or in a change in the specificity of the enzyme toward its substrates.